The present invention relates in general to the field of electrical power distribution systems. More particularly, the present invention relates to reclosers and sectionalizers.
A common problem in almost any electrical power distribution system is a momentary disruption of electrical service, such as might be caused by a momentary short circuit. For example, power lines strung between poles could swing under wind loading, momentarily touching each other or a grounded conductor. Things may fall across exposed wires, arcing could occur, or other transitory events could cause momentary power line short circuits or current surges which could burn out a fuse or trip a circuit breaker. Most of these faults are self correcting and do not require permanent fuse or circuit breaker protection because they terminate quickly. If a fuse should burn out or a circuit breaker should trip, the power line would be open and customers would be deprived of their electrical power. Service calls to replace fuses or reset circuit breakers would then be required, thus escalating the customer""s costs.
A recloser is a fault-interrupting device used to sense current, voltage, and/or frequency and isolate faulted portions of distribution feeders. A recloser is operated by a recloser control device, which can be an electronic control circuit. Reclosers are inserted into power lines to protect a power distribution system.
More particularly, reclosers are electromechanical devices, similar to circuit breakers. Reclosers are distributed at one or more locations along a power line, typically upline from a fuse. When a fault condition is detected by the recloser controller, the recloser will begin to timeout. In other words, the recloser controller will trip open the recloser if the fault condition has not cleared itself during a fixed time interval, where the time interval is a function of current. Then, as the name suggests, the recloser will close, and if the fault condition has been cleared, power service will resume. If, however, the fault condition has not been cleared, the recloser controller will again trip open the recloser after a second fixed time interval. If, after a predetermined number of reclose operations, the fault condition has not been cleared, the recloser controller will permanently lockout the recloser (i.e., permanently open the circuit). The circuit then remains open until the system is repaired and/or the fault condition is eliminated.
A recloser senses the peak value of the current conducted and interrupting its flow by opening or tripping a recloser before a fuse blows. After an interval, the recloser closes, thereby restoring power to the system where it remains closed until the next fault is sensed.
It must also be recognized that some faults which occur on a power distribution line are temporary, such as those caused by a branch momentarily falling against the line. Some faults are of a more permanent nature such as those caused by a line falling to the ground. As a consequence, reclosers are programmed so that they will trip a limited number of times within a short duration before locking open.
At some magnitude of fault current it is desirable to have the recloser open immediately to protect the line rather than following a time current characteristic. At intermediate fault levels it may be desirable from the power distribution standpoint to delay opening the recloser to allow the fault to clear itself or a fuse to operate. Many reclosers have alternate time current characteristics which achieve this goal.
Conventional reclosers for three-phase systems open all three phases at the same time upon detection of a fault on any one phase. Other three-phase systems implement three single-phase reclosers, one on each phase. A recloser can interrupt high currents.
A recloser controller provides the intelligence that enables a recloser to sense overcurrents, select timing operations, time the tripping and reclosing functions, and lockout.
A sectionalizer is a load or no-load opening device that is used to isolate portions of an electrical network. A sectionalizer cannot interrupt high currents, it can only open and close, like a switch. A sectionalizer is typically implemented in series with one or more reclosers and typically operates after a recloser has opened for a fault and there has been a predetermined dead time, thereby allowing the sectionalizer to open before the recloser closes.
It is difficult to coordinate several (e.g., more than three) reclosers in a row. Accordingly, it would be desirable provide recloser control that can adaptively control a recloser to function as a recloser or as a sectionalizer, depending on the currently prevailing conditions, in order to assist in coordination.
The present invention is directed to systems and methods for setting a recloser to act as a recloser or a sectionalizer, in response to prevailing conditions. The prevailing conditions that are determined are those that will affect the operation of the recloser, such as the number of faults, the fault current versus time, or the presence of reverse power.
The foregoing and other aspects of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.